Nematic liquid crystal composition

ABSTRACT

A nematic liquid crystal composition includes a compound of formula (1) and a host mixture:  
                 
 
wherein ‘R’ is chosen from C n H 2n+1 O, C n H 2n+1 , C n H 2n+1 S or C n H 2n−1 ; ‘n’ is an integer of 1 to 15; ‘A’ is  
                 
 
‘a’ is 0 or 1; ‘B’ is —CH 2 CH 2 —, —C═C—, —C≡C— or  
                 
 
‘b’ is 0 or 1; ‘D’ is  
                 
 
—CH 2 CH 2 —, —C═C— or —C≡C—; ‘d’ is 0 or 1; ‘X’ is H, F, Cl, Br, NCS or CN; and ‘Y’ is from NCS, SCN or F. A liquid crystal display apparatus employing the nematic liquid crystal composition has a high response speed and a high phase transition temperature. In addition, the nematic liquid crystal composition has an augmented birefringence and a dielectric anisotropy. The liquid crystal display apparatus using the nematic liquid crystal composition may have an enhanced brightness.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relies for priority upon Korean Patent Application No.2003-46513 filed on Jul. 9, 2003, the contents of which are hereinincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nematic liquid crystal composition.More particularly, the present invention relates to a nematic liquidcrystal composition having a high phase transition temperature and ahigh response speed.

2. Description of the Related Art

Recently, an information processing technology and a technology ofmanufacturing information processing devices have been developed. Withdevelopments of the technologies, a massive data may be processed inshort time. Thus, a display device that displays the processed data hasbeen introduced in various fields.

With a rapid development of a semiconductor technology, electronicdevices are demanded to be small in size, light, in weight and low powerconsumptive. In recent years, a flat panel display apparatus with theabove characteristics is in strong demand.

In particular, demands for a liquid crystal apparatus device haveincreased since the liquid crystal display device requires low powerconsumption and low operation voltage while exhibiting an excellentdisplay quality as bright as a display apparatus using a cathode raytube. The liquid crystal display apparatus is widely used in variouselectronic devices.

The liquid crystal display apparatus may be applied to display devicessuch as a notebook computer, a computer monitor or a television set. Asfor the television set, a twisted nematic (TN) liquid crystal displayapparatus, an in-plane switching (IPS) liquid crystal display apparatusor a vertical alignment (VA) mode liquid crystal display apparatus maybe used. The IPS liquid crystal display apparatus and the VA mode liquidcrystal display apparatus have a wide viewing angle, but a slow responsespeed. Thus, the IPS liquid crystal display apparatus and the VA modeliquid crystal display apparatus may not be suitable for displaying amoving image. In addition, manufacturing yields of the apparatuses arelow and manufacturing costs of the apparatuses are high.

Alternatively, the TN liquid crystal display apparatus has a highmanufacturing yield and a low manufacturing cost. The TN liquid crystaldisplay apparatus, however, has a narrow viewing angle and a lowresponse speed.

Liquid crystal requires a low viscosity for a high response speed, ahigh dielectric anisotropy for low operation voltage, and a nematicphase over a wide range of temperature. Birefringence of the liquidcrystal is preferably at least about 0.20 at about 25° C.

Generally, each of the TN liquid crystal display apparatus, the IPSliquid crystal display apparatus and the VA mode liquid crystal displayapparatus has a response speed of about 20 ms to about 30 ms. Anincrease of the response speed in the above apparatuses, however, isrequired for displaying a moving image.

A viewing angle of a liquid crystal display apparatus has been improvedby use of a compensation film. The response speed, however, primarilydepends on characteristics of the liquid crystal. Thus, a novel liquidcrystal composition that exhibits a high response speed is required.

To display an image in the liquid crystal display apparatus as brightlyas a display apparatus using the cathode ray tube, a backlight assemblyis used as a light supply source. The backlight assembly, however, maygenerate a heat in the lamp tube of the backlight assembly.

Generally, a liquid crystal display apparatus has two substrates and aliquid crystal layer interposed between the two substrates. Electricpower from an external power supply is applied to electrodes on thesubstrates. The liquid crystal transmits or blocks an external lightgenerated from the backlight assembly to display data as an image. Thebacklight assembly is disposed near the liquid crystal. Thus, the heatgenerated from the backlight assembly may be transferred to the liquidcrystal.

Accordingly, a liquid crystal composition with a high phase transitiontemperature is required. Currently used nematic liquid crystalcompositions for a TN liquid crystal display apparatus, an IPS liquidcrystal display apparatus or a VA mode liquid crystal display apparatusmay have a phase transition temperature of about 70° C. to about 80° C.,which is not preferable for a display apparatus requiring a highbrightness.

SUMMARY OF THE INVENTION

Accordingly, the present invention is provided to substantially obviateone or more problems due to limitations and disadvantages of the relatedart.

The present invention provides a nematic liquid crystal composition witha high response speed and a high phase transition temperature.

According to an exemplary composition of the present invention, anematic liquid crystal composition including a compound of formula (1)and a host mixture is provided:

wherein R is C_(n) _(2n+1)O, C_(n)H_(2n+1), C_(n)H_(2n+1)S orC_(n)H_(2n+1); n is an integer of 1 to 15; ‘A’ is

‘a’ is 0 or 1; ‘B’ is CH₂CH₂—, —C═C—, —C≡C— or

‘b’ is 0 or 1; ‘D’ is

—CH₂CH₂—, —C═C— or —C≡C—; ‘d’ is 0 or 1; ‘X’ is H, F, Cl, Br, NCS or CN;and ‘Y’ is NCS, SCN or F.

The nematic liquid crystal composition has relatively high phasetransition temperature and response speed. In addition, the nematicliquid crystal composition has an augmented birefringence and adielectric anisotropy. The liquid crystal display apparatus using thenematic liquid crystal composition may have an enhanced brightness.

DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail.

A nematic liquid crystal composition according to the present inventionincludes a compound of formula (1) and a host mixture.

The compound in the nematic liquid crystal composition is represented bythe formula (1):

wherein ‘R’ is C_(n)H_(2n+1)O, C_(n)H_(2n+1), C_(n)H_(2n+1)S orC_(n)H_(2n+1); ‘n’ is an integer of 15; ‘A’ is

‘a’ is 0 or 1; ‘B’ is CH₂CH₂—, —C═C—, —C≡C— or

‘b’ is 0 or 1; ‘D’ is

—CH₂CH₂—, —C═C— or —C≡C—; ‘d’ is 0 or 1; ‘X’ is H, F, Cl, Br, NCS or CN;and ‘Y’ is NCS, SCN or F.

When the contents of the nematic liquid crystal composition include lessthan about 1% by weight of the compound of formula (1), a desired effectof the nematic liquid crystal composition may be not obtained. When thecontents of the nematic liquid crystal composition exceed about 90% byweight of the compound of formula (1), the nematic liquid crystalcomposition may not satisfy a characteristic of high response speed forliquid crystal. Therefore, the nematic liquid crystal compositionincludes preferably about 1% to about 90% by weight of the compound offormula (1) and about 10% to about 99% by weight of a host mixture.

As mentioned above, the nematic liquid crystal composition includes thecompound of formula (1) and the host mixture. The host mixture includescompounds of formulae (2) to (15):

wherein R₁ is methyl; R₂ is ethyl; R_(2d) is vinyl; R₃ is propyl; R_(3d)is allyl; and R₅ is pentyl.

Alternatively, the host mixture includes compounds of formulae (2) to(8) and (12) to (18):

wherein R₁ is methyl; R₂ is ethyl; R_(2d) is vinyl; R₃ is propyl; R_(3d)is allyl; and R₅ is pentyl.

Hereinafter, the present invention will be described in detail withreference to the following examples. The examples are given solely forthe purpose of illustration and are not to be construed as limitationsof the present invention, as many variations thereof are possiblewithout departing from the spirit and scope of the invention.

A first host mixture used in Examples includes about 6.6% by weight ofthe compound of formula (2), about 5.4% by weight of the compound offormula (3), about 20.8% by weight of the compound of formula (4), about4.1% by weight of the compound of formula (5), about 11.07% by weight ofthe compound of formula (6), about 2.5% by weight of the compound offormula (7), about 2.5% by weight of the compound of formula (8), about3.4% by weight of the compound of formula (9), about 9.0% by weight ofthe compound of formula (10), about 9.4% by weight of the compound offormula (11), about 8.66% by weight of the compound of formula (12),about 8.0% by weight of the compound of formula (13), about 3.6% byweight of the compound of formula (14) and about 4.97% by weight of thecompound of formula (15).

In examples, a phase transition temperature (Tni) indicates atemperature at which liquid crystal is changed from a liquid crystalphase to an isotropic liquid phase.

EXAMPLE 1

About 7% by weight of the compound of formula (1-1) and about 93% of thefirst host compound were mixed to prepare a liquid crystal composition.

The liquid crystal composition had a phase transition temperature (Tni)of about 87.9° C. The liquid crystal composition has a birefringence(Δn) of about 0.0909 and a dielectric anisotropy (Δε) of about 6.1 atabout 20° C.

The compound of formula (1-1) had a melting point of about 97.8° C. anda phase transition temperature (Tni) of about 192.5° C. The compound offormula (1-1) had a birefringence (Δn) of about 0.302 and a dielectricanisotropy (Δε) of about 12.

EXAMPLE 2

About 17% by weight of the compound of formula (1-1) and about 83% ofthe first host compound were mixed to prepare a liquid crystalcomposition.

The liquid crystal composition had a phase transition temperature (Tni)of about 96° C. The liquid crystal composition had a birefringence (Δn)of about 0.115 and a dielectric anisotropy (Δε) of about 6.68 at about20° C.

The compound of formula (1-1) had a melting point of about 97.8° C. anda phase transition temperature (Tni) of about 192.5° C. The compound offormula (1-1) had a birefringence (Δn) of about 0.302 and a dielectricanisotropy (Δε) of about 12.

EXAMPLE 3

About 30% by weight of the compound of formula (1-1) and about 70% ofthe first host compound were mixed to prepare a liquid crystalcomposition.

The liquid crystal composition had a phase transition temperature (Tni)of about 113.8° C. The liquid crystal composition had a birefringence(Δε) of about is 0.1431 and a dielectric anisotropy (Δε) of about 7.5 atabout 20° C.

The compound of formula (1-1) had a melting point of about 97.8° C. anda phase transition temperature (Tni) of about 192.5° C. The compound offormula (1-1) had a birefringence (Δn) of 0.302 and a dielectricanisotropy (Δε) of about 12.

EXAMPLE 4

About 7% by weight of a compound of formula (1-2) and about 93% of thefirst host compound were mixed to prepare a liquid crystal composition.

The liquid crystal composition had a phase transition temperature (Tni)of about 90.3° C. The liquid crystal composition had a birefringence(Δn) of about 0.0899 and a dielectric anisotropy (Δε) of about 6.3 atabout 20° C.

The compound of formula (1-2) had a melting point of about 109.7° C. anda phase transition temperature (Tni) of about 227.6° C. The compound offormula (1-1) had a birefringence (Δn) of about 0.288 and a dielectricanisotropy (Δε) of about 14.7.

EXAMPLE 5

About 17% by weight of the compound of formula (1-2) and about 83% ofthe first host compound were mixed to prepare a liquid crystalcomposition.

The liquid crystal composition had a phase transition temperature (Tni)of about 103.5° C. The liquid crystal composition had a birefringence(Δε) of about 0.115 and a dielectric anisotropy (Δε) of about 7.14 atabout 20° C.

The compound of formula (1-2) had a melting point of about 109.7° C. anda is phase transition temperature (Tni) of about 227.6° C. The compoundof formula (1-1) had a birefringence (Δn) of about 0.288 and adielectric anisotropy (Δε) of about 14.7.

EXAMPLE 6

About 30% by weight of the compound of formula (1-2) and about 70% ofthe first host compound were mixed to prepare a liquid crystalcomposition.

The liquid crystal composition had a phase transition temperature (Tni)of about 124.3° C. The liquid crystal composition had a birefringence(Δn) of about 0.1389 and a dielectric anisotropy (Δε) of about 8.4 atabout 20° C.

The compound of formula (1-2) had a melting point of about 109.7° C. anda phase transition temperature (Tni) of about 227.6° C. The compound offormula (1-1) had a birefringence (Δn) of about 0.288 and a dielectricanisotropy (Δε) of about 14.7.

EXAMPLE 7

About 17.7% by weight of a compound of formula (1-3) and about 82.3% ofthe first host compound were mixed to prepare a liquid crystalcomposition.

The liquid crystal composition had a phase transition temperature (Tni)of about 101.5° C. The liquid crystal composition had a birefringence(Δn) of about 0.111 and a dielectric anisotropy (Δε) of about 6.65 atabout 20° C.

The compound of formula (1-3) had a melting point of about 87.4° C. anda phase transition temperature Tni of about 215° C. The compound offormula (1-3) had a birefringence (Δn) of about 0.274 and a dielectricanisotropy (Δε) of about 11.5.

EXAMPLE 8

About 7% by weight of a compound of formula (1-4) and about 93% of thefirst host compound were mixed to prepare a liquid crystal composition.

The liquid crystal composition had a phase transition temperature (Tni)of about 89.5° C. The liquid crystal composition had a birefringence(Δn) of about 0.0899 and a dielectric anisotropy (Δε) of about 6.1 atabout 20° C.

The compound of formula (1-4) had a melting point of about 90° C. and aphase transition temperature (Tni) of about 216° C. The compound offormula (1-4) had a birefringence (Δn) of about 0.274 and a dielectricanisotropy (Δε) of about 12.1.

EXAMPLE 9

About 17% by weight of the compound of formula (1-4) and about 83% ofthe first host compound were mixed to prepare a liquid crystalcomposition.

The liquid crystal composition had a phase transition temperature (Tni)of about 102° C. The liquid crystal composition had a birefringence (Δn)of about 0.111 and a dielectric anisotropy (Δε) of about 6.41 at about20° C.

The compound of formula (1-4) had a melting point of about 90° C. and aphase transition temperature (Tni) of about 216° C. The compound offormula (1-4) had a birefringence (Δn) of about 0.274 and a dielectricanisotropy (Δε) of about 12.1.

EXAMPLE 10

About 30% by weight of the compound of formula (1-4) and about 70% ofthe first host compound were mixed to prepare a liquid crystalcomposition.

The liquid crystal composition had a phase transition temperature (Tni)of about 120.8° C. The liquid crystal composition had a birefringence(Δn) of about 0.1347 and a dielectric anisotropy (Δε) of about 7.6 atabout 20° C.

The compound of formula (1-4) had a melting point of about 90° C. and aphase transition temperature (Tni) of about 216° C. The compound offormula (1-4) had a birefringence (Δn) of about 0.274 and a dielectricanisotropy (Δε) of about 12.1.

EXAMPLE 11

About 6.3% by weight of the compound of formula (2), about 5.2% byweight of the compound of formula (3), about 20.1% by weight of thecompound of formula (4), about 4.4% by weight of the compound of formula(5), about 6.8% by weight of the compound of formula (13), about 2.4% byweight of the compound of formula (8), about 2.9% by weight of thecompound of formula (15), about 3.3% by weight of the compound offormula (16), about 8.7% by weight of the compound of formula (17),about 9.1% by weight of the compound of formula (18), about 2.9% byweight of the compound of formula (7), about 7.2% by weight of thecompound of formula (12), about 2.3% by weight of the compound offormula (14), about 10.2% by weight of the compound of formula (6),about 4% by weight of the compound of formula (1-1) and about 4.2% byweight of the compound of formula (1-2) were mixed to prepare a liquidcrystal composition.

The liquid crystal composition had a phase transition temperature (Tni)of about 89° C. The liquid crystal composition had a birefringence (Δn)of about 0.094 and a dielectric anisotropy (Δε) of about 6.3 at about20° C.

COMPARATIVE EXAMPLE 1

A liquid crystal composition including the first host mixture wasprepared. The liquid crystal composition had a melting point of about−30° C. and a phase transition temperature (Tni) of about 80° C. Theliquid crystal composition had a birefringence (Δn) of about 0.075 and adielectric anisotropy (Δε) of about 5.63.

Evaluating Characteristics of Liquid Crystal Compositions

Liquid crystal display apparatuses were manufactured using the liquidcrystal compositions of Comparative Example 1, Examples 2, 5, 7, 9 and11. A response speed, a threshold voltage, a voltage holding ratio and acell gap were evaluated for each liquid crystal display apparatus. Theresults are shown in Table 1 below. TABLE 1 Response speed ThresholdVoltage holding Cell gap (ms) voltage (V) ratio (%) (μm) Comparative16.2 — — 4.6 Example 1 Example 2 9.0 1.5 99.4 3.77 Example 5 9.4 1.499.0 3.7 Example 7 9.9 1.5 99.1 3.7 Example 9 11.0 1.4 99.1 3.7 Example11 12.0 1.5 99.8 4.0

Referring to Table 1, the threshold voltages are not very differentbetween Examples. Voltage holding ratios are also not very differentfrom each other between Examples. The liquid crystal composition ofExample 2 shows the fastest response speed. The liquid crystalcomposition of Comparative Example 1 includes a conventional liquidcrystal composition. As shown in Table 1, the liquid crystalcompositions of Examples 2, 5, 7, 9 and 11 give response speeds at least4 ms faster than the conventional liquid crystal composition.

The liquid crystal composition of Example 2 has the phase transitiontemperature (Tni) of about 96° C., which is at least about 15° C. higherthan that of Comparative Example 1, i.e., about 80° C.

The compounds of formulae (1-1) to (1-4) have the phase transitiontemperatures (Tni) of about 190° C. to about 220° C., which are at leasttwice of that in Comparative Example 1 of about 80° C. The compounds offormulae (1-1) to (1-4) have birefringence of at least about 0.2 that ishigher than the conventional liquid crystal composition, andanisotropies of at least about 10, thereby reducing operation voltages.

In Examples 1 to 10, the phase transition temperatures (Tni) of theliquid crystal compositions increase as content of the compoundaccording to the present invention increases.

The compound used in a nematic liquid crystal composition has highbirefringence, high phase transition temperature and fast responsespeed. Thus, the nematic liquid crystal composition may maintaincharacteristics thereof when the heat generated in the backlight isprovided to the liquid crystal composition.

The liquid crystal composition according to the present invention may beused in a twisted nematic liquid crystal display apparatus, a supertwisted nematic liquid crystal display apparatus, a thin film transistortwisted nematic liquid crystal display apparatus, an in-plane switchingliquid crystal display apparatus and a vertical alignment mode liquidcrystal display apparatus.

As described above, the present invention provides a liquid crystalcomposition including the compound of formula (1):

wherein ‘R’ is C_(n)H_(2n+1)O, C_(n)H_(2n+1), C_(n)H_(2n+1)S orC_(n)H_(2n+1); ‘n’ is an integer of 1 to 15; ‘A’ is

‘a’ is 0 or 1; ‘B’ is —CH₂CH₂—, —C═C—, —C≡C— or

‘b’ is 0 or 1; ‘D’ is

—CH₂CH₂—, —C═C— or —C≡C—; ‘d’ is 0 or 1; ‘X’ is H, F, Cl, Br, NCS or CN;and ‘Y’ is NCS, SCN or F.

The liquid crystal composition including the compound of formula (1) hasa relatively high phase transition temperature and response speed. Inaddition, a birefringence and a dielectric anisotropy of the liquidcrystal composition are increased, thereby providing a liquid crystaldisplay apparatus with high brightness. As a result, a liquid crystaldisplay apparatus having excellent performance may be provided.

1. A nematic liquid crystal composition comprising a compound of formula(1) and a host mixture:

wherein ‘R’ is any one selected from the group consisting ofC_(n)H_(2n+1)O, C_(n)H_(2n+1), C_(n)H_(2n+1)S and C_(n)H_(2n−1); ‘n’ isan integer of 1 to 15; ‘A’ is any one selected from the group consistingof

‘a’ is 0 or 1; ‘B’ is any one selected from the group consisting of—CH₂CH₂—, —C═C—, —C≡ C— and

‘b’ is 0 or 1; ‘D’ is any one selected from the group consisting of

—CH₂CH₂—, —C═C— and —C≡C—; ‘d’ is 0 or 1; X is H, F, Cl, Br, NCS or CN;and Y is NCS, SCN or F.
 2. The nematic liquid crystal composition ofclaim 1, wherein the nematic liquid crystal composition comprises about1% to about 90% by weight of the compound of formula (1) and about 10%to about 99% by weight of the host mixture.
 3. The nematic liquidcrystal composition of claim 1, wherein the host mixture comprisescompounds of formulae (2) to (15):

wherein R₁ is methyl; R₂ is ethyl; R_(2d) is vinyl; R₃ is propyl; R_(3d)is allyl; and R₅ is pentyl.
 4. The nematic liquid crystal composition ofclaim 1, wherein the host mixture comprises compounds of formulae (2) to(8) and (12) to (18):

wherein R₁ is methyl; R₂ is ethyl; R_(2d) is vinyl; R₃ is propyl; R_(3d)is allyl; and R₅ is pentyl.
 5. The nematic liquid crystal composition ofclaim 1, wherein the nematic liquid crystal composition is used in atwisted nematic liquid crystal display apparatus.
 6. The nematic liquidcrystal composition of claim 1, wherein the nematic liquid crystalcomposition is used in a super twisted nematic liquid crystal displayapparatus.
 7. The nematic liquid crystal composition of claim 1, whereinthe nematic liquid crystal composition is used in a thin film transistortwisted nematic liquid crystal display apparatus.
 8. The nematic liquidcrystal composition of claim 1, wherein the nematic liquid crystalcomposition is used in an in-plane switching liquid crystal displayapparatus.
 9. The nematic liquid crystal composition of claim 1, whereinthe nematic liquid crystal composition is used in a vertical alignmentmode liquid crystal display apparatus.